The invention relates to the field of drive technology and is directed to an apparatus for stabilizing the speed of a motor. A phase comparator is provided having a sample-and-hold element and a sampling pulse shaper connected therewith and input with a speed signal. The phase comparator identifies the phase difference between a reference signal and the speed signal that acquires the speed of the motor and generates an output signal proportional to the identified phase difference. A controller is input with the output signal. A control circuit for the motor is connected to the controller.
Such an apparatus is known, for example, from the textbook "Halbleiter-Schaltungen", Tietze/Schenk, Axel Springer Verlag, 9th Edition, pages 954-959. The PLL control described therein makes it possible to couple a DC motor to a reference signal in phase-locked fashion, given employment of a phase comparator. Such controls, however, usually have a dead zone that opposes a high-precision control. This dead zone results since the known phase comparators only offer a pulse sequence that has a pulse width proportional to the phase difference. The pulse sequence is smoothed in a following RC element that represents an integrator. The pulse width, however, cannot become arbitrarily narrow and thereby simultaneously has properties proportional to the phase difference. Due to the employment of non-ideal components and running or transit times resulting therefrom, a minimum width of the pulses must thus be taken into consideration.